The Optimum Design of Stratified Thermal Energy Storage Systems—Part II: Completion of the Analytical Model, Presentation and Interpretation of the Results

[+] Author and Article Information
R. J. Krane

Department of Mechanical and Aerospace Engineering, The University of Tennessee, Knoxville, TN 37996-2210

M. J. M. Krane

Physical Technology Group, Semiconductor and Interconnect Technology, Digital Equipment Corporation, Andover, MA 01810

J. Energy Resour. Technol 114(3), 204-208 (Sep 01, 1992) (5 pages) doi:10.1115/1.2905942 History: Received February 15, 1991; Revised December 12, 1991; Online April 16, 2008


This investigation is presented in two parts. The basic analytical model is developed in Part I. Part II includes the completion of the analytical model and the results of an optimization study performed with this model. The results show that: 1) Significant performance gains, that is, reductions in the entropy generation number on the order of 10 percent, are possible by employing perfectly stratified thermal energy storage systems that are designed on the basis of the second law of thermodynamics. 2) These performance gains are mainly due to the complete elimination of the entropy generation due to heat transfer through finite temperature differences within the storage element. 3) In general, the optimum design of a perfectly stratified thermal energy storage system requires the use of a very large heat exchanger; however, it is possible to employ a much smaller than optimum heat exchanger without seriously degrading the superior performance of the system. 4) The operation of a stratified system is quite flexible because it has no optimum storage time. 5) The optimum values of the capacity rate ratios, (φR )opt and (φR )opt , for a perfectly stratified thermal energy storage system are in general not equal to unity; however, this finding is shown to be in concert with Bejan’s theory of “remanent” irreversibilities for a heat exchanger.

Copyright © 1992 by The American Society of Mechanical Engineers
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